Question

I have this table:

Month    Type
JAN        A
JAN        A
FEB        B
FEB        B
FEB        A
FEB        A

I want to run a query that groups by month and counts the occurrences of a type for that month.
So for the table above, the output should be:

        A     B
JAN     2     0
FEB     2     2

It’s probably not possible, but thought I’d give it a shot.
Thank you.

Answer 1

Unfortunately MySQL does not have a PIVOT function which is basically what you are trying to do. So you will need to use an aggregate function with a CASE statement:

SELECT Month,
  SUM(case when type = 'A' then 1 ELSE 0 END) as A,
  SUM(case when type = 'B' then 1 ELSE 0 END) as B
FROM yourTable
GROUP BY month

See SQL Fiddle with Demo

Now if you want to perform this dynamically, meaning you do not know ahead of time the columns to transpose, then you should review the following article:

Dynamic pivot tables (transform rows to columns)

Your code would look like this:

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'SUM(case when type = ''',
      type,
      ''' then 1 ELSE 0 END) AS ',
      type
    )
  ) INTO @sql
FROM test;

SET @sql = CONCAT('SELECT month, ', @sql, ' FROM test GROUP BY month');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

See SQL Fiddle with Demo